> 1. Is it correct that just because a mode is listed in the NBEMS mode > list, does not mean that you could not use it with flarq as an ARQ mode?
Yes, but some modes cannot be used as an ARQ mode due to either too much latency or ascii or control code support. The only modes tested with flarq are DominoEx, MFSK16,32,64, PSK31,63,125,250, Thor (all speeds) and MT-63-2000. The latency of MT-63 is so great, only the fastest speed is enough to enable ARQ to work. > > Therefore, any of the modes could theoretically be used, even if not > recommended or even if they might not work very well but flarq will ARQ > any of them? See above. Of the available modes for ARQ, the ones listed for NBEMS are the ones recommended for messaging. However, on VHF when signals are near the noise, it is sometimes easier to tune with PSK31 (because the idle carriers stand out more clearly against the noise background on the waterfall than the multi-tone modes) and then switch to MFSK16 or DominoEx11 without changing the tuning. > > 2. Could you explain how the MFSK modes are made more robust and yet can > still work with other programs? We worked with ZL1BPU, one of the authors of MFSK16, to implement several enhancements, one of which is called "puncturing", which averages the signal level and if a signal sample is significantly above the average, it is assumed to be a static burst and the AFC is momentarily disabled. The fldigi MFSK modes are compatible with MFSK16 or MFSK8 in other programs, but it is necessary to use fldigi in order to get the advantage of the enchancements. > > On another note, thanks for confirming what I suspected about the drift > issue. I recently was told that I my preference for purchasing only TCXO > rigs was overkill, even for VHF, but when you look at the ppm issues > with modes such as MFSK, even a few Hz is a problem. Generally, not on HF so much, as transceivers tend to have less drift on HF, especially on 80m and 40m, but definitely on VHF, where excessive drift can often be a serious problem for some digital modes. 73, Skip KH6TY NBEMS Development Team
